|Can your other two PC's ping the server?|
Assuming your "server" contains all shares and shared data, can the other two PC's access that data?
If the answer to the above is "yes" then you have no issue and chances are, whatever it is you're trying to ping from the server has it's built in firewall running and that is set to not respond to ICMP (ping) requests.
It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.